Challenge on Combustion

CFD Simulation of combution

AIM

The aim of this study is to analyze the combutionof the methane fuel in the presence of air and water particle and investigate the different emissions Product produce after burning the methane and to find the effect of water adding to fuel on the emissions.

INTRODUCTION

Combustion is the chemical reaction of fuel and air. The application of combustion are aircraft propulsion system, power plant, automobile engine, furnace etc. Therefore it is required to model the combustion of fuel. There are different approaches to simulate the combustion.

Types of combustion simulation

Based on Mixing

• Non premixed combustion (Direct injection, Late injection)Example of this combustion is spark ignition petrol engine.
• Premixed combustion (Carburetor).Example of this combustion is aircraft gas turbine, furnace diesel engine.
• Partially premixed. Example of this combustion is direct injection petrol engine.

Based on phase

• Fluid phase (Vometric reactions)
• Wall (surface reacions)
• Particles (surface reaction)
• Porous region (Example: after treatment system)

In this present simulation, Volumetric reaction was taken as for simulation.

Geometry

The 3D model of the combuster is shown in Figure 1. In this model, small fuel inlet was given at the center and large air inlet was given.This 3D model was imported in ANSYS Spaceclaim. This model is very large so number of mesh elements will be more so its computational cost will be more so for this model, Axisymmetric simulation was done using 2D model or one slice of this cylinder as shown in Figure 2.

Figure 1. 3D model of combuster

Figure 2. 2D model of combuster

MESH GENERATION

Mesh generation of this model was carried out using ANSYS MESHER. Tringular method was taken for mesh generation. The numbers of elements were 9236. For refine the mesh near the fuel, default value taken for capture proximity. Meshing of this model and meshing details showed in Figure 3 and Figure 4.

Figure 3. Mesh generation2D model of combuster

Figure 4. Mesh details of 2D model of combuster

This model was imported in solver ANSYS Fluent for the simulation. There are two types of Axisymmetric simulation were carried out with this model. In the first part, there are only air and fuel combustion occur inside burner. There are Nox and soot produce during this combustion. In the second part, 15% water was added in the fuel by mole and simulation was carried out to investigate the effect on the Nox and soot. The pressure based solver used and steady state simulation was carried out with 800 iterations.

Boundary condition

In this model, two inlets, air and fuel were there. In the part 1, mole of fuel was taken as one wheres in the part 2, 15% water was added in the fuel by mole. methan was taken as the fuel.

Air inlet velocity - 1 m/s

Fuel inlet velocity - 85 m/s

species transport model was enable and Volumetric reaction was carried out in this combustion. During this process, Fuel was ignite by eddy dissipation.

RESULTS

This steady state simulation was carried out for 800 iteration. Figure 5. showed the graph between iteration vs. residuals. In the postprocessing, different charts and contours are shown below.

Part I

In the part I, only fuel methane and air were in the combustion preocess. Figure 6 showed the contour of temperation on the XY Plane of the model.

Figure 5. Iteration vs. residuals

Figure 6. Temperature contour

Maximum temperature, during this combustion was 2309.74 K. There are uniform temperature distribution at the outlet as shown in figure 6. Animation of temperature is shown below.

Figure 7. mass fraction of methane

Figure 7. showed the mass fraction of methane. there are different lines were drawn at different distance from the inlet of air. On this line different charts were drawn to see the variation of mass fraction of different components on Y axis as shown in Figure 8.

Figure 8. lines on plane

from the air inlets, distance of lines are 0.15 m, 0.3 m, 0.45 m, 0.6 m, 0.75 m and 0.8 m.

Figure 9. Variation of mass fraction of methane

Figure 10. Contour of mass fraction of CO2

Figure 11. Variation of mass fraction of CO2

Figure 12. Variation of mass fraction of H20

Figure 13. Variation of mass fraction of N2

Figure 14. Contour of mass fraction of O2

Figure 15. Variation of mass fraction of O2

Figure 16. Contour of mass fraction of NO

Figure 17. Variation of mass fraction of NO

Figure 18. mass fraction contour of soots

Figure 19. Variation of mass fraction of soot

Figure 20. mass fraction Contour of N2O

Figure 21. Variation of mass fraction of N2O

Animation of Nox produce as shown below.

PART 2

Fuel - methane

15% water added in fuel by mole

Figure 22. Temperature contour on XY plane

Maximum temperature reached after the combustion was 2231 K. so after the water added, maximum temperature decreases about 78.74 K.

Figure 23. mass fraction of methane on XY plane

Figure 24. Variation in mass fraction of methane

Figure 25. mass fraction of CO2 on XY plane

Figure 26. Variation in mass fraction of CO2

Figure 27. mass fraction of N2O on XY plane

Figure 28. Variation in mass fraction of N2O

Figure 29. mass fraction of NO on XY plane

Figure 30. Variation in mass fraction of NO

Figure 31. Variation in mass fraction of SOOT

Figure 32. mass fraction of N2 on XY plane

Figure 33. mass fraction of O2 on XY plane

Figure 34. Variation in mass fraction of O2

Figure 35. mass fraction of H2O on XY plane

Conclusion

From this simulation in both the parts, It is conclude that temperature distribution at the outlet is uniform. In part I, maximum temperature reached about 2309 K whereas in Part II maximum temperature reached about 2231 K so there were 78.74 K decrease in temperature with 15% water in Fuel by mole.

It is also conclude that with adding water in fuel, there was no change in CO2 product and O2. At the outlet the emissions distribution becomes uniform.

There were decreases the emissions of NOx and soot with adding 15% water in fuel.